Influence of the elements (Pn = As, Sb, Bi) on the transport properties of p-type Zintl compounds Ba2ZnPn2

In our work, we calculated the relaxation times of Ba(2)ZnPn(2) (Pn = As, Sb, Bi) based on the deformation potential (DP) theory using the first-principles method, and successfully predicted high thermoelectric performance (ZT > 2) along z-direction for p-type Ba2ZnAs2 and Ba2ZnSb2. The Seebeck coefficient (5) of Ba2ZnAs2 monotonously increases with increasing temperature, which is favorable for achieving high thermoelectric performance in high temperature range. We also find that the four approximately degenerated bands (N-v = 4) near the valence band edge mainly originating from the interaction between Zn atoms and Pn atoms, and the different strengths of Zn Pn bonding lead to the different energy range spanned of the four bands. The weak Zn As bonding decreases the dispersion of the four bands, which leads to a sharply increased total density of states near the valence band edge, and will largely increase the S of Ba2ZnAs2, while the strong Zn Bi bonding increases the dispersion of the four bands near the VB edge, which reduces the effective mass of valence bands near the VB edge, and will be in favor of the carrier mobility. The coexistence of two heavy bands and two light bands near the VB edge contributes to their simultaneous high Seebeck coefficients and high electrical conductivities at the optimum carrier concentration. Moreover, their electrical conductivities along the z-direction are much higher than those along the x- and y-directions, possibly originating from the chain-like arrangement of covalent ZnPn(4) tetrahedra. (C) 2016 Elsevier B.V. All rights reserved.